A variety of refractory articles are used in the casting of steel and other metals. These refractory articles include crucibles, kiln furniture, launder blocks, lentel blocks, nozzles, pouring cups, pouring tubes, pump tubes, shrouds, stopper rods, and tundishes. These refractory articles in the metal casting process are subjected to very harsh and corrosive working environments. They must be able to withstand hours exposed to molten metals. They must also be capable of enduring the harsh thermal shock encountered on the start-up of casting and the buoyant forces.